1. Field of the Invention
The present invention relates to an electromagnetic linear driving device of a linear motor type, which is used as a speedometer or tachometer for automobiles, a driver for the linear tracking arm of record players, a driver for line printers, and the like.
2. Description of the Prior Art
A prior art electromagnetic linear driving device comprises a stationary magnetic member, a winding coiled around the stationary magnetic member in the longitudinal direction thereof, and a permanent magnet movable along the stationary magnetic member (See Japanese unexamined utility model publication (kokai) No. 55-170879). The permanent magnet generates a magnetic flux which links some turns of the winding. When a current is supplied to the winding, the current flowing through the turns of the winding interacts with the magnetic flux generated by the permanent magnet such as to move the permanent magnet. Additionally, the current flowing through each turn of the winding generates a magnetic flux within the stationary magnetic member.
In the above-mentioned prior art, therefore, when the stroke, i.e., the distance the permanent magnet moves, is increased without reducing the driving force, the cross-section of the stationary magnetic member must be increased in proportional to the increase in the stroke. This is because an increase in the stroke causes an increase in the number of turns of the stationary magnetic member, i.e., an increase in the magnetic flux within the stationary magnetic member. Therefore, in order to avoid saturation of the magnetic flux within the stationary magnetic member, if the stroke of the permanent magnet is doubled, the cross-section of the stationary magnetic member is also doubled, and the weight thereof is increased four fold, which is a disadvantage.